1. Field
One embodiment of the present invention relates to an information recording medium capable of recording and reproducing information by using a short-wavelength laser beam such as a blue laser beam and, more particularly, to a write-once information recording medium, an information recording medium capable of recording information in multiple layers, and a disk apparatus using the information recording medium.
2. Description of the Related Art
Optical disks are roughly classified into three types of disks, i.e., a ROM disk for playback only, a write-once R disk, and a rewritable RW or RAM disk. As the volume of information increases, optical disks are being required to have large capacities and high transfer rates. To meet the market demand for large capacities, a DVD-R disk having two recoding layers instead of a normal single recording layer is being developed in order to increase the capacity even when using a recording system using the same laser wavelength.
To further increase the capacity of an optical disk, an optical disk called an HD DVD has been developed. The data capacity of one side of an HD DVD-ROM or HD DVD-R is 15 GB that is three times or more the data capacity of the conventional DVD, i.e., 4.7 GB. An organic dye material is used in a recording layer of this HD DVD-R as described in, e.g., Jpn. Pat. Appln. KOKAI Publication Nos. 2006-205683 and 2005-271587.
Unfortunately, forming two recording layers in this HD DVD-R is much more difficult than forming two recording layers in the DVD-R because the density is high. In particular, the deterioration of signal characteristics in the outer circumference is serious.